Growing Tomatoes Outdoors for Profit – Complete Outdoors Tomato Growing Guide

Summary of Tomato Farming

Tomato farming techniques – Tomato farming guide

Growing tomatoes outdoors –if done rationally and on a scalable basis- can be a good source of income. In a few words, tomato is a perennial plant, but growers usually treat it as an annual. Most commercial tomato growers start the crop from seeds (hybrids) in an indoor protected environment. They prepare the field as they wait for the young seedlings to grow and be ready for transplanting (normally 30-50 days). They till the land and remove any previous cultivation remains. Some growers place a black plastic film on the ground. This plastic film helps the soil become warmer and controls weeds. Moreover, before planting, tomato producers design and set the irrigation system, which usually is drip irrigation.

When they are ready for transplanting, they make small holes in the plastic film, where they plant the seedlings. Fertilization, Drip Irrigation, and Weed Management are applied in most cases. When plants reach a height of 40 cm (16 inches), most growers stake the plants, mainly the indeterminate varieties. If not, the plants cannot support their weight and further develop (this does not apply for processed tomato varieties). Producers may also apply thinning in some table varieties. This means that commercial tomato growers remove some fruits at their early development stages. They do so to encourage the plant to devote its resources to fewer but bigger and tastier fruits. 

Most tomato varieties can be harvested 7-10 weeks after transplanting. The time from planting to harvesting depends on the variety, climate conditions, and the age of the seedlings planted. Producers harvest tomatoes through hand scissors or knives typically in 2-3 sessions per week. This does not apply to tomatoes intended for canning. Producers harvest the industrial (processed) tomatoes mechanically at one session because the tractor-attached harvesting machine destroys the plant completely. After harvesting, tomato growers destroy the remaining of the crop. Crop rotation is crucial in tomato farming. When it is possible, producers rotate the crop (with cabbage, corn, legumes and others), in order to control diseases and prevent soil from depleting. 

The restrictive factor when growing tomatoes outdoors is usually the temperature. The plant requires on average temperatures from 18 to 26 °C (64.4 to 78.8 °F), while soil temperature should not fall below 14 °C (57 °F). Low temperature during the growth period will inhibit the procedure. It is nearly impossible for shocked plants to recover. 

It is crucial to decide on the growing method as well as the varieties of tomatoes that thrive in our area.  There are three methods to grow tomatoes: Growing from seed, growing from non-grafted seedlings, and growing from grafted seedlings.

How to Grow Tomatoes From Seed

Tomato is a warm-season crop. Tomatoes plants need, on average, 7-10 weeks from transplanting to harvest. However, if you are planning to grow tomatoes from seed, there are some facts you need to know. First, tomato seeds require a temperature of at least 21 °C (70 °F) in order to germinate. Secondly, the seeds need to have optimum moisture levels in order to sprout. Excessive irrigation can turn disastrous. Producers in areas with risk of frost prefer to sow the seeds in seedbeds under controlled conditions and then transplant them into their final positions. On average, we need 120-150 grams of seeds per hectare (1 hectare = 10.000 square meters = 2,47 acres).

How to Grow Tomatoes from Non-Grafted Seedlings

Another method is growing tomatoes from non-grafted plants. If we follow this method, it is crucial to choose carefully the variety of tomatoes we are going to plant. If -for example- the fields in our area have problems with soil-borne diseases, pests, extreme pH or salinity levels, then not all varieties can thrive. Some varieties are tolerant to some of those factors, while others are not. 

How to Grow Tomatoes from Grafted Seedlings

Nowadays, a significant number of growers prefer to use grafted tomato seedlings. In a few words, grafting is a commonly used technique through which we join together parts from two different plants so that they will grow as a single plant. The upper part of the first plant is called a scion and grows on the root system of the second plant, which is called the rootstock.  Eventually, we have a plant that combines all the advantages of its different components. Some experienced producers, with specialized knowledge, prefer to grow from seed, both the plant intended to be the rootstock and the plant intended to be the scion. Then, they perform the grafting by themselves. Others prefer to buy certified grafted seedlings from legitimate sellers. 

Soil Requirements for Tomato Farming

Tomatoes do not have strict soil requirements. They grow well in various soils, provided they drain well. However, the plant thrives best in medium sandy soils with proper aeration and drainage. The plant is sensitive to both drought and water-soaked conditions. The optimum pH levels range from 6 to 6.5.

The basic soil preparation starts a few weeks before transplanting tomato seedlings. Farmers remove any previous crop remains and weeds and plow well at a depth of 60 cm (23.6 inches). Plowing improves soil aeration and drainage. At the same time, they remove rocks and other undesirable materials from the soil. One week later, many farmers apply a basal fertilizer such as well-rotted manure or synthetic commercial fertilizer after examining their soil test results and consulting a local licensed agronomist. Most farmers integrate top dressing on the same day with tilling. Some producers prefer to apply top dressing only across the planting lines, while others apply it to the entire field. Of course, the first method is more cost-saving. The next day is probably the right time to install the drip irrigation pipes. The next and most crucial step (especially in countries with low soil temperatures during planting) is the linear polyethylene coating. Many producers cover the rows with black or green infrared-transmitting (IRT) or black plastic film. They use this technique to maintain the root zone temperature at optimum levels (>21 °C or 70 °F) and prevent weeds from growing. 

Tomato Planting, Plant spacing and Number of Plants per Hectare 

In many tomato-producing countries, the best season for planting outdoor tomatoes is usually during the middle of the second half of spring. However, in some areas where temperatures are high enough, planting can certainly take place earlier. On the other hand, in northern areas, producers usually plant their tomatoes during early summer. 

In many cases, the young seedlings must undergo a ” hardening ” procedure before transplanting. Hardening is practically a kind of artificial stress. It may involve temperature change or other techniques and is performed to help the plant better adapt to new conditions. Producers usually cause water stress by gradually reducing the water supply to their plants. Producers stop the water supply a few hours before transplanting (13-15 hours) and then irrigate again immediately after transplanting. Tomato producers keep their seedlings in seedbeds 30-50 days before transplanting them into their final positions. Producers prefer to transplant seedlings that are 3-6 weeks old. At this stage, the plants have an average height of 20 cm (8 inches) and have 3-5 true leaves.

After all the preparation steps (plowing, basal fertilization, irrigation system installation and plastic film covering), we can proceed with transplanting. The growers label the exact spots on the plastic film or directly on the soil where they will plant the young seedlings. Then, they dig holes and plant the seedlings. Planting the seedlings at the same depth as they were in the nursery is important. 

Outdoors, tomato farmers usually plant their seedlings in single rows. A common pattern for single-row planting is 0.3 m to 0.6 m (12-24 inches) distance between plants on the row and 0.8 m to 1.3 m (2.6-4.3 ft) distance between rows. For twin-row planting, growers maintain the same distance between plants on the row, 0.45 m (1.48 ft) distance between rows and 1.2 m (3.94 ft) between two couples. We will have approximately 15000-30000 plants per hectare following these patterns. The exact distances and the number of plants depend on the tomato variety, environmental conditions, the irrigation system, and, of course, the yield goals of the producer. (1 hectare = 2,47 acres = 10.000 square meters).

How to Prune Tomatoes

Pruning is one of the most important farming practices for determinative tomato varieties. It provides several advantages. First of all, pruning enables farmers to monitor and balance the vegetation and fruit set of plants. Furthermore, pruning facilitates aeration that prevents infections. Moreover, harvesting and other farming techniques (spraying of chemicals) become much more accessible. 

Generally, unpruned tomato plants stop producing sufficient fruits after a given time. We need to understand that not all tomatoes need the same pruning. Generally, we have two main tomato types: determinate and indeterminate. Indeterminate varieties need heavier pruning than determinate varieties to grow correctly. A common pruning technique includes the removal of the outer stems, leaving only the central vein to grow. This way, the plant becomes single-veined and expands only vertically. Another technique is the dead-heading of the plant during the early stages of its development, followed by the removal of peripheral stems except for 2-4. Thus, the plant develops 2-4 main stems. 

Most producers also apply thinning. They remove the stems that grow between the vein and the foliage. Trying not to cut the stem too close to the vein is crucial. Instead, you can consider leaving a 4 cm distance to avoid infections. For outdoor tomato farming, several varieties have limited growth and do not need pruning. 

Tomato Stacking

Most tomato producers stake their tomatoes. Especially when it comes to indeterminate varieties, staking is almost always required. There are several advantages to the use of this technique. First, it prevents foliage and fruits from touching the ground while leaving extra space for aeration. Moreover, harvesting has become much more accessible. The right time to start stacking is when tomatoes have reached an average height of 40 cm (16 inches). 

Farmers place the stakes linearly next to each plant and gently tie the plants over them. They can also place a wire every 30 cm (11.8 inches) for about 1.5 meters (59 inches) in height. The wire is placed perpendicular to the piles and parallel to the lines.

Tomato Water Requirements -Tomato Irrigation Systems

Outdoor tomato farming may require up to 700 mm of irrigation water during a growing season. Much of the water needed in outdoor crops is covered by rainwater. However, tomato water requirements are different during the various development stages of the plant. In general, the critical periods for irrigation are during flowering, fruit set, and fruit filling. Before those stages, water requirements were smaller.

Of course, water requirements can be different under different weather and soil conditions. For example, heavy clay soils normally need less irrigation than sandy soils. On the other hand, different tomato varieties may also have different water requirements.

Many producers have reported that they irrigate their plants for 10 minutes every 4-5 days during winter and every two days during summer, at the first stages of the plant development. In this way, they force the plant to ‘seek’ water and, as a result, develop a deeper rooting system. They follow this pattern until the setting of the 3rd inflorescence. From this point and until harvesting, they irrigate their plants almost daily.

Farmers generally prefer to water their tomatoes early or late in the evening. Watering the foliage has been linked with disease outbreaks. Excess humidity, especially on foliage, may favor disease outbreaks. On the other hand, water-stressed plants are more susceptible to infections.

The most commonly used irrigation system is drip irrigation. Many producers use multiple or single drip pipes of 12-20 mm diameter. These can provide a water supply of 2-8 liters per hour.

Tomato Fertilization Requirements – Best Tomato Fertilizer

First, you must consider the soil condition of your field through semi-annual or annual soil testing before applying any fertilization method. There are no two identical fields in the world. Thus, nobody can advise you on fertilization methods without considering your soil’s test data, tissue analysis and crop history of your field. However, we will list some standard tomato fertilization programs that are used by farmers.

According to an old general rule in tomato farming, plants need an average of 300 kg N, 85 kg P₂O₅, 480 kg K₂O, 30 CaO, and 18 kg MgO per hectare (= 2.47 acres).

Farmers generally make from 0 to 10 fertilizer applications throughout the 2 to 3 months period from transplanting to harvesting. Many farmers apply well-rotted manure towards the rows about two months before planting. They also use pre-planting fertilization high in nitrogen a couple of days before planting. 

However, the most common tomato fertilization method is fertigation. Producers inject water-soluble fertilizers inside the drip irrigation system. In this way, they can provide the nutrients gradually and give the plant the proper time to absorb them. 

A few days after planting, they start the fertigation. They apply nitrogen- Phosphorus- Potassium fertilizer (13-40-13 or 15-30-15) enriched with trace elements (micronutrients). High Phosphorus levels at the first stages will help plants develop a robust root system. Additionally, micronutrients make it easier for plants to overcome any stress conditions caused by transplanting. 

They continue the applications, adding Ca every three days until the 3rd inflorescence set. During the following days, they changed the Nitrogen- Phosphorus- Potassium ratio to 1-1-2. When the fruits reach maturity, they change the ratio to 1-1-3. From this point, they increase Potassium levels because plants have a higher need for potassium to create big, well-shaped fruits.

According to another fertilization program, the four most important stages of the tomato crop cycle are the following:

1.) Leaf Development Stage (2 to 15 days after transplanting)

2.) Flowering Stage (16 to 30 days after transplanting)

3.) Fruit Setting Stage (31 to 41 days after transplanting)

4.) Fruit Growth Stage (day 42 to harvest)

During these periods, the total fertilizer application in kg via fertigation includes: 

• During Periods 1 and 2 (29 days), they apply 16 kg N, 4 kg P₂O₅, 24 kg K20, and 2 kg CaO. 
• During period 3 (11 days in total), they applied 6 kg of N, 2 kg of P₂O₅, 8 kg of K20, and 1 kg of CaO. 
• During period 4 (fruit growth phase), fertilization rates increase dramatically, and farmers apply 20 kg N, 6 kg P₂O₅, 35 kg K₂O, and 2 kg CaO. These quantities are total (not daily amounts) counted in kilograms per hectare of the total area of the farm.

However, these are just some standard practices. No one should follow them without personal research. Every field is different and has different needs. Checking the soil condition and pH is vital before applying any fertilization method. You can consult your local licensed agronomist.

Outdoor Tomato Harvesting and Storage

Most tomatoes reach their full maturity and are ready for harvesting 7-10 weeks after transplanting, depending on the tomato variety, the environmental conditions, the age of the transplants and other farming techniques. 

Producers mechanically harvest the industrial tomatoes (processed tomatoes intended for sauces and canning) at one session. In most cases, this occurs late in summer. On the contrary, tomatoes that will be sold for raw consumption (table varieties) are usually collected by hand, along with the calyx and part of the pod. Farmers usually harvest these tomatoes one or two stages before the final ripening stage. This is essential for tomatoes that will be transported over long distances. The harvest period may last several weeks, so farmers harvest on average 2-3 times per week.

Outdoor Tomato Yields

Yields on outdoor tomato farming on stalked crops are on average 60-100 tonnes per hectare (53.553 – 89.255 lbs per acre). Determinate varieties, however, do not usually yield more than 30-50 tonnes per hectare (26.776 -44.627 lbs per acre) due to their smaller crop cycle. Industrial outdoor tomatoes from experienced professional growers usually yield 60-80 tonnes per hectare (53.553 – 71.404 lbs per acre). These are average yields, and there are impressive deviations in many cases.

Τomatoes are collected and categorized depending on their size, shape, and overall condition. They are then transferred to cool but not freezing (13°C – 55.4°F) storage areas, so that a potential weight loss is avoided. Tomatoes can be stored in colder conditions (4°C – 39.2°F) provided they have been collected during their final stages of maturity. If not, the tomatoes will fail to reach the desired maturity level. They will probably not acquire an intense red color because the production of substances responsible for giving red color to the fruit stops at low temperatures.

Most common Tomato Nutrient Deficiencies

Understanding that a plant nutrient deficiency does not necessarily mean the soil is depleted is crucial. Plant deficiencies occur due to various environmental or other factors that lead to the plant’s inability to absorb this specific nutrient. Thus, farmers should consider testing soil and tissue before taking any corrective action. Only after receiving the results from the laboratory will producers be able to discuss the solution to the problem with the agronomist.

N-Deficiency

Tomato plants with N deficiency express their problem with symptoms such as discoloration of older leaves. We observe yellow leaves at this part of the foliage soon after the deficiency has begun. A few days later, the entire plant turns light green and often has reduced development. The reasons for such a deficiency may include increased potassium or phosphorus levels or excess soil humidity levels.

K-Deficiency  

The symptoms of potassium deficiency often appear with characteristic interveinal chlorosis. Older foliage may wilt and turn brown and scorched. Some of the reasons for K-deficiency are higher than normal organic matter content, increased magnesium or calcium levels, prolonged drought, low pH levels, increased EC levels, or low temperatures. 

Ca-Deficiency

The most commonly recognized symptom caused by Ca- deficiency is blossom end rot. By this, we refer to a flat brown area at the fruit blossom end, that may appear at any fruit development stage. The commercial value of the fruits decreases rapidly in this case. Blossom end rot is an ideal environment for secondary fungal infections. Some of the Ca-deficiency causes include extended applications of Nitrogen fertilizers, root injuries that make it difficult for the plant to absorb Calcium, rapid fluctuations of soil water levels, too much Potassium, Magnesium or Sodium, low pH levels, or heavy rainfalls during a short period.

Physiological Anomalies of Tomatoes

Sunscald

Sunscald is caused by extended exposure to sunlight from fruit. Tomatoes develop a characteristic yellow-to-white area with thin, dried skin at the surface directly exposed to sunlight. The cause of this anomaly is the abnormal foliage-to-fruit ratio. 

Leafroll  

Leafroll disorder is believed to appear due to a lack of humidity caused by prolonged drought and heat or other stress factors such as heavy pruning or sudden plant growth. It is a common problem in tomatoes that grow in greenhouses. 

Fruit Cracks

Fruit cracks are injuries of the fruit caused by sudden and increased water absorbance, especially after a prolonged drought. 

Common Tomato Pest and Diseases 

Pests

Tuta absoluta

A few years ago, no one had heard about Tuta. Yet, now it is perhaps the most severe enemy for tomato producers. Tuta absoluta originated in South America and is a highly disastrous Lepidoptera for tomatoes. It also attacks other Solanaceae, like potatoes, without causing them such damage. The pest appeared in countries around the Mediterranean in 2006, and now is one of the biggest nightmares of tomato growers in most tomato-producing areas globally. Adults lay their eggs under the foliage, stems, or fruits. Young larvae start feeding on them. The foliage or stems collapse, and fruits lose their commercial value.

Once the crop has been attacked, management is more complicated. Since Tuta develops immunity against pesticides very easily, biological management is the best method to control it. Pheromone traps are a commonly used technique. They attract male insects, preventing them from fertile females. Thus, they somehow reduce their population.

Liriomyza

Lyriomyza spp is an insect that causes extensive damage in many plants, including tomatoes. The damage caused by this fly is similar to the damage by Tuta absoluta. Adults puncture the leaves, the stems, and the fruits and lay their eggs. After hatching, young larvae start to feed by the tissues, causing characteristic white mines. The damage reduces the quality and commercial value of the fruit. Management includes most of the measures suggested for Tuta absoluta. 

Tetranychus 

Tetranychus urticae is a tiny spider mite that attacks many crops, including tomatoes. Spiders overwinter in leaf debris and attack tomatoes during hot and dry weather conditions. Mites attack the foliage to feed, causing yellow discolorations or a characteristic bronze-brown wilt that resembles flame damage. We may also observe webs between the foliage.

A proper technique is to monitor the population using traps constantly. If the number exceeds tolerable limits, you may consider intervening always after consulting a local licensed agronomist. There are biological as well as chemical solutions on the market, which, of course, should always be used under Good Agricultural Practices standards.

Tomato Diseases

Botrytis (Grey Mold)

Grey mold is a severe tomato disease, caused by the fungus Botrytis cinerea. The pathogen can survive for long periods in the form of sclerotia. Infections are favored by low temperatures and high humidity levels, while wind and rain spread the spores from plant to plant. Symptoms may appear to all the overground parts of the plant; however, healthy tissue is not infected actively. Infections occur to injured tissue, for instance, after pruning. Symptoms include grey to brown lesions formed at the edges of leaves. After a while, these lesions are covered in grey mold. Injured tissue may develop cankers that girdle the veins leading to the death of the plant. If the fruit is indeed infected, then it turns soft and water-soaked.

Disease control begins with proper precautionary measures. The most crucial step is crop rotation. Then, weed control and safe distances between plants are important. Adequate pruning at the right time and being careful not to water the foliage are also precautionary measures. The general condition of the plants (nutrients and water level, sun exposure) can also boost their immunity. Chemical treatment is used only if the problem is severe and always under supervision from a local licensed agronomist. It is also crucial to use proper sanitation, such as tools disinfection every time we touch the plants.

Alternaria (Early Blight)

It is a serious tomato disease caused by the fungus Alternaria solani. The pathogen overwinters on crop debris, seeds or weeds and is spread through air and water. Alternaria infects tomatoes at several development stages. Symptoms include seedlings rot, stem cankers, and others. In order to manage the infection, there are some precautionary measures to consider such as crop rotation, weed control, plant debris removal, drip irrigation and use of resistant tomato varieties. 

Late Blight (Phytophthora infestans)

Heavy rainfalls during late spring or early summer in many countries is a serious sign that the disease will be spread rapidly in large commercial outdoor tomato farms. Infected tomato plants can be destroyed by P. infestans. Tomato fruits have dark brown spots that gradually grow and destroy the whole tomato fruit.

Anthracnose

Anthracnose is another common tomato disease caused by the fungi Colletotrichum spp. The pathogen may infect all plant parts; however, we often observe symptoms on ripen fruits. Immature fruits may have been contaminated, but symptoms are not visible yet. Symptoms on ripening tomatoes appear as white circular lesions periodically enlarge, and turn brown. 

Powdery Mildew

Unlike most fungi tomato diseases, Powdery Mildew, although favored by high humidity, can develop during dry periods. We can see white powdery mildew of fungal mycelium on the upper surface of the leaves. Symptoms may also include green chlorotic angular lesions on the upper surface of the leaves. We must always disinfect our tools after handling an infected plant to prevent the infection from spreading to healthy plants. Management includes all the Botrytis control measures combined with resistant plants.

Verticillium Wilt

This wilt is caused by the fungi Verticillium albo-atrum and V. dahliae. The pathogen survives in plant tissue and can be transmitted by nematodes.  The pathogen invades the plant through the roots. We must be careful because the disease can be asymptomatic during the first stages, making it more difficult to manage later. The disease destroys the plant’s vascular system. Water and nutrients cannot be transferred to the upper parts of the tomato plant. At the last stages of the disease cycle, we observe foliage wilting during hot days. Leaves also develop chlorosis and angular, v-shaped lesions.

Tomato spotted wilt (TSWV)

The disease of TSWV is also essential. Thrips are the most common TSWV transmitters. Symptoms include dark spots on foliage and streaks in stems. If the infection occurs before the fruit set, the plant will probably fail to produce fruits. Unfortunately, it has been observed that the virus also infects weeds immediately after tomato cultivation. This, unfortunately, plays a crucial role in preserving the pathogen even when the field remains fallow.

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